In electrosurgery, a high-frequency electric current is passed through biologic tissues to achieve specific surgical effects such as cutting, coagulation, or desiccation. Electrosurgery allows cutting while at the same time controlling the amount of bleeding. Cutting is achieved primarily with a continuous sinusoidal waveform, whereas coagulation is achieved primarily with a series of sinusoidal wave packets. A surgeon using an electrosurgical unit (ESU) selects either one of these waveforms or a blend of them to suit the surgical needs.
An electrosurgical unit can be operated is two modes, the monopolar mode and the bipolar mode. The most noticeable difference between these two modes is the method in which the electric current enters and leaves the tissue. In the monopolar mode, the current flows from a small active electrode into the surgical site, spreads though the body, and returns to a large dispersive electrode on the skin. The high current density in the vicinity of the active electrode achieves tissue cutting or coagulation, whereas the low current density under the dispersive electrode causes no tissue damage. In the bipolar mode, the current flows only through the tissue held between two forceps electrodes. The monopolar mode is used for both cutting and coagulation. The bipolar mode is used primarily for coagulation.
The effects of electrosurgery are based on the rapid heating of tissue. When tissue is rapidly heated above 45.degree. C., irreversible changes take place that inhibit normal cell function and lead to cell death. First, between 45.degree. C. and 60.degree. C., the proteins in the cell lose their quaternary configuration and solidify into a glutinous substance that resembles the white of a hard-boiled egg. This process, termed coagulation, is accompanied by tissue blanching. Further increasing the temperature up to 100.degree. C. leads to tissue drying; that is the aqueous cell contents evaporate. This process is called desiccation. If the temperature is increased beyond 100.degree. C., the solid contents of the tissue reduce to carbon, a process referred to as carbonization.
In the monopolar mode, the active electrode either touches the tissue directly or is held a few millimeters above the tissue. It is important to note that the blade edge does not cut the tissue with an electrosurgical blade. Rather, it is the electric current which does the cutting. When the electrode is held above the tissue, the electric current bridges the air gap by creating an electric discharge arc. A visible arc forms when the electric field strength exceeds 1 kV/mm in the gap. The temperature inside a discharge location is of an order of thousands of degrees Centigrade, causing the formation of a plasma, which evaporates the tissue being cut. If the plasma does not have a chance to evacuate quickly, the trapped plasma will evaporate a larger pocket of tissue, thus creating a the larger wound. One problem with conventional electrosurgery blades is that this arcing is unstable as the arcs initiate from various locations on the blade edge and surface. The arc will typically initiate from somewhere on the blade edge since the electric current will tend to flow through the sharpest location on the electrode. This instability requires greater current and thus more localized heating of the tissue. Thus, it would be an advancement in the art to provide an active electrode capable of discharging electric current with a substantially uniform distribution. It would also be desirable to reduce the size of the cutting wound caused by the electrosurgical blade.
A problem with the use of electrosurgery blades is that of undesirable current concentration due to contact between the active electrode and the tissue. This is exacerbated by the tendency of some bare metal electrodes to stick to tissue. When an electrode sticks to tissue, much or all of the electrical current discharged from the electrode may pass through the same portion of the patient's body. The resulting burns may substantially increase the patient's healing period. In addition, of course, tissue is damaged when a sticking electrode is pulled away from the tissue. This problem has been addressed in part in the prior art with the use of various "non-stick" coatings such as silicon, Teflon.RTM. and titanium nitride. It would be desirable to further reduce the problem of tissue sticking by reducing the heating of the electrode separate from or in addition to such coatings. It would thus be an advancement in the art to provide an active electrode for electrosurgery that required less current for cutting.
One of the more undesirable properties of electrosurgery is the smoke which is generated by cutting which interferes with the ability of the surgeon to view the cut. Various designs have been developed to blow or suction the smoke away from the region of the cut. It would be desirable to provide a blade which substantially reduces the amount of smoke generated in connection with cutting using an electrosurgical blade.